Common standards of steel casing pipe

Oil steel casing pipe is a thin-walled steel pipe used for oil and natural gas transportation in oil pipelines, oil wells and gas wells. Steel casing is used as the well wall of oil and gas wells. It can withstand high pressure, high temperature and corrosive media. The following are some major oil steel casing standards:

1. API 5CT: The API standard is an oil steel casing pipe standard developed by the American Petroleum Institute and is one of the widely used oil casing standards in the world. API 5CT specifies the requirements for the classification, technical conditions, test methods, marking, packaging and transportation of oil casing. According to the API standard, oil casing is divided into multiple steel grades such as H40, J55, K55, N80, L80, C90, C95, P110 and Q125, each of which has its specific mechanical properties and uses.

2. ISO 11960: The oil casing pipe standard developed by the International Organization for Standardization is similar to API 5CT and includes different grades of casing.
3. GB/T 9711.1: Petroleum casing standards formulated by China National Organization for Standardization, including L175, L210, L245, L290, L320, L360, L390, L415,
L450, etc.

4. SY/T 6194: SY/T standards are petroleum casing standards formulated by China's petrochemical industry standards, including two types, Casing and Tubing, which are used at different depths and conditions of oil wells and are mainly used for the production and inspection of domestic petroleum casing. These standards specify the size, chemical composition, mechanical properties, quality requirements, packaging and transportation requirements of petroleum casing to ensure its safety and reliability in the process of oil and gas extraction. The length of domestic casing ranges from 8-13 meters, but casing not shorter than 6 meters can be provided, and the quantity shall not exceed 20%‌.

API 5CT steel casing pipe size standards:

According to the API 5CT specification, the oil casing pipe size standards mainly include the following aspects:

1. Outer diameter (OD): According to the API 5CT specification, the outer diameter of the oil casing can range from 2.375 inches to 20 inches, among which the common outer diameters are 4.5 inches, 5 inches, 5.5 inches, 7 inches, etc.
2. Wall thickness: The wall thickness of the oil casing varies according to the different outer diameters and materials, usually in the range of 0.224 inches to 1.000 inches.
3. Steel grade: The API 5CT specification defines multiple steel grades for oil casing, including H40, J55, K55, N80, L80, C90, T95, P110, etc. Different steel grades have different mechanical properties and corrosion resistance.
4. Connection method: API 5CT specification also specifies the connection methods of casing, including external thread (EUE) and internal thread (NU). These connection methods can meet the different requirements of casing in well construction and oil and gas production.
5. Length: API 5CT specification specifies the length of oil casing within the range, usually R1 (18-22 feet), R2 (27-30 feet) and R3 (38-45 feet), etc.

The above are the common size standards of oil casing in API 5CT specification. According to the specific use requirements and geographical conditions, the appropriate casing size and steel grade can be selected. These size standards can ensure that the quality and performance of the casing meet international standards, and are suitable for different types of oil and gas well construction and production.

Types of oil steel casing pipe:

Oil casing pipe plays a vital role in the process of oil drilling and extraction. According to its functions and usage scenarios, it can be mainly divided into the following categories:

1. Conductor Casing
The conductor is the first casing lowered into the well. It is usually used to isolate the shallow water layer on the surface, prevent the backflow of drilling fluid, and support the weight of subsequent casing.

It is usually located at a shallow position below the surface, mainly used for wellhead protection in the early stage of drilling and the establishment of drilling fluid circulation channels.

2. Surface Casing
The surface casing is located below the conductor and is used to isolate the unstable soft formations, formations that are prone to collapse and leakage, and water layers on the upper part.

It can support part of the weight of the subsequent technical casing and oil layer casing, and provide a stable working environment for subsequent drilling operations.

3. Technical casing (Intermediate Casing)
Technical casing is also called intermediate casing, which is used to isolate the difficult-to-control complex formations, serious leakage layers, and oil, gas, and water layers with large pressure differences encountered during drilling.

It helps to maintain the stability of the wellbore, prevent the wellbore from expanding, and provide safety conditions for complex drilling operations such as directional wells.

4. Oil layer casing (Production Casing)
Oil layer casing is also called production casing, which is the deepest casing with the smallest diameter.

It is used to isolate the target layer from other formations, establish an oil and gas channel, and ensure that oil and gas can be smoothly exported from the formation to the ground. The depth of the oil layer casing usually depends on the depth of the target layer and the completion method.

In addition to the above main categories, other types of casing may also be required according to the specific drilling process and geological conditions, such as liner, protective casing, etc. These casings have their own specific usage scenarios and functions, and together constitute the casing system in the process of oil drilling and production.

How to choose the right oil steel casing pipe?

‌The following key factors need to be considered when choosing steel casing‌ pipe:

‌1. Material selection‌
Oil casing can be divided into steel pipes, cast iron pipes and plastic fiber pipes according to the material. Casings of different materials are suitable for different application scenarios. For example, plastic fiber pipes and cast iron pipes have low strength and are suitable for shallow holes and water wells; spiral welded pipes are suitable for deep hole drilling; high-grade seamless steel pipes are suitable for deep hole drilling and long-term monitoring holes‌.

‌2. Steel grade selection‌
Oil casing is divided into different steel grades according to the strength of the steel itself, such as J55, K55, N80, L80, C90, T95, P110, Q125, V150, etc. The selection of the right steel grade depends on the depth of the borehole and the geological conditions. For example, low-grade seamless steel pipes are suitable for boreholes with a depth of 1000 to 2000 meters, while high-grade seamless steel pipes should be selected for boreholes deeper than 2000 meters‌.

‌3. Type selection‌

According to the usage, oil casing can be divided into guide tube, surface casing, technical casing and oil layer casing. Different types of casing are suitable for different formations and operation requirements. For example, guide tube is used to protect the wellhead, surface casing is used to protect the shallow formation, technical casing is used to protect the intermediate formation, and oil layer casing is directly in contact with the oil and gas layer. ‌

‌4. Standard and specification selection‌

The specifications and standards of oil casing are also very important. Common standards include API (American Petroleum Institute) standards and SY/T domestic standards. Choosing appropriate specifications and standards requires considering specific engineering requirements and geological conditions. For example, API standard products are usually of high quality and reliability, suitable for high-demand engineering projects. ‌

Specifications: According to the diameter and length of the oil pipe to be protected, select the corresponding specifications of the casing to ensure that the oil pipe can be fully covered. ‌ Thickness: Thickness is one of the important indicators for measuring casing quality. Casing with moderate and uniform thickness should be selected to ensure its strength and wear resistance. ‌ Production process: Choose a casing with exquisite production technology, tight braiding, smooth surface and no burrs to ensure its quality and reliability.

It should be noted that different types of casings may differ in material, size, wall thickness, etc. to adapt to different use environments and requirements. Therefore, when selecting and using steel casings, comprehensive considerations and decisions need to be made based on specific circumstances.

Read more: OCTG Casing Pipe Size Chart or Casing pipe VS Drill pipe